Flight-Testing Europe’s Huge New Turboprop

Before the long-delayed first flight of the A400M, the new airlifter’s TP400 turboprop was flown 18 times on a C-130 flight test bed (FTB) modified and flown by Marshall Aerospace. This was a challenging task, since the TP400 produces 2.5 times the thrust of a C-130’s standard T56 engine and weighs twice as much. Marshalls had to build a “pilot-in-the-loop” simulator from the cockpit of a retired C-130K and perform extensive aerodynamic modeling and computational fluid dynamics analysis before the aerodynamic differences of the C-130 FTB versus a standard C-130K could be estimated.

To accept the huge TP400 on the inner left wing position, the center wing had to be reinforced and a three-part pylon designed. Damping struts linking the pylon to the fuselage were added, mainly because of the prop flutter concerns. There was less than 11 inches clearance between the C-130 fuselage and the TP400’s eight-bladed, 17.5-foot diameter propeller. Inside the FTB, the flight deck was rebuilt to add new caution and warning lights, an additional throttle box for the TP400 and two panels for an engine indication and crew alerting system.

The structural mods were completed in March 2007 and a dummy engine was fitted, pending the arrival of the real thing late that year. The propeller arrived in early 2008. All four engines were ground run for the first time in June 2008. After 24 hours of ground runs, followed by low- and high-speed taxi trials, the C-130 FTB finally made its first flight on Dec. 17, 2008.

After 18 flights and 55 hours, plus another 61 hours ground-running, the TP400 flight-test program on the C-130 was wrapped up on September 30 last year. According to Boyle and Young, the primary objectives set by Airbus Military were to identify any Fadec issues; to measure propeller stress in the different rpm modes; to check the nacelle ventilation; to explore engine failure modes, feathering and the relight capability; and to measure noise and vibration. These objectives were all met, they added.

Airbus Military has subsequently told AIN that a propeller measurement scheduled for the C-130 FTB was deferred to the A400M flight test program. This caused a delay in mid-January, when wet weather in Seville meant that the moisture-sensitive prop sensors could not be flown. Marshalls told AIN that some testing was intentionally deferred due to the differences in the flight envelope between the A400M and the FTB; however, all scheduled testing on the FTB was completed. (For more detailed A400M coverage, go to www.tinyurl.com/A400Mtrials.)